In an electrophotographic process which has been most generally practiced at present, an amorphous selenium series photoreceptor and an organic photoreceptor are used as the photoreceptor. However, these photoreceptors are lacking in the crystallization, the mechanical characteristics, and panchromatic property.
Recently, as an electrophotographic photoreceptor, a photoreceptor having a photoconductive layer mainly composed of amorphous silicon is proposed. The photoreceptor having the photoconductive layer mainly composed of amorphous silicon is excellent in hardness, heat stability, and chemical stability, as compared with the amorphous selenium photoreceptor and the organic photoreceptor described above, and hence is expected to become a long-life photoreceptor having a high sensitivity.
Amorphous silicon is a photoconductor showing both polarities and is expected to be used as a positive-charging type photoreceptor and a negative-charging type photoreceptor for a electrophotographic photoreceptor, as described, e.g., in JP-A-1-179166 (the term "JP-A" as used herein means as "unexamined published Japanese patent application").
However, with the recent propagation of a negative-charging type organic photoreceptor, many systems using a developer for a negative-charging system have been investigated and practically used, and there occurs a problem in that the amorphous silicon photoreceptor which has hitherto been practically used as a positive-charging photoreceptor can not be applied to the negative-charging system.
JP-B-64-9625 and JP-B-64-962 (the term "JP-B" as used herein means an "examined published Japanese patent application") disclose a positive-charging or negative-charging electrophotographic photoreceptor comprising an amorphous silicon photoconductive layer having a hydrogen atom content of from 1 to 40 atomic %, and an amorphous silicon charge injection inhibition layer (interlayer) having a hydrogen atom content of from 0.25 to 35 atomic % and a nitrogen atom content of from 25 to 55 atomic %, which is provided between the amorphous silicon photoconductive layer and a substrate.
The composition of the interlayer as disclosed is shown by a-(Si.sub.x N.sub.1-x).sub.y :H.sub.1-7, and the value of x must be in the range of from 0.43 to 0.60. The ratio of N/Si of the interlayer becomes 1.32 when x is 0.43 and the ratio becomes 0.66 when x is 0.60. That is, the interlayer containing from 0.66 to 1.32 by atomic ratio of a nitrogen atom to a silicon atom is disclosed. It is also described that the thickness of the interlayer is in the range of from 30 to 1,000 .ANG. (0.003 to 1 .mu.m).
The function as the interlayer is to improve the charge blocking property (charge injection prevention), and the improvement of the charge blocking property can be realized by reducing the amount of nitrogen in the interlayer, but the reduction of the amount of nitrogen in the interlayer is accompanied by a secondary hindrance, such as the increase of the residual electric potential of the photoreceptor. Accordingly, for practically using such a photoreceptor, it is required to reduce the thickness of the interlayer 0.1 .mu.m or less. However, the reduction of the thickness of the interlayer brings direct contact of the photoconductive layer and the substrate, due to dusts attached onto the substrate upon production of the photoreceptor, in particular, dusts over 0.1 .mu.m in diameter. The direct contact of the photoconductive layer and the substrate causes a partial injection of a charge into the photoconductive layer, which causes a defect of the device and also the defect of the image quality. Therefore, the problem of the dust gives large influences on the yield at the production of the photoreceptors.